Scientists Discover First Omnivorous Shark That Loves Eating Plants

Generally, sharks are archetype killers – often the apex predators of their environment, known for ripping prey to shreds. However, the bonnethead shark (Sphyrna tiburo) swims its own path. Scientists have discovered that it is an omnivore, the first known instance of a shark eating plants. It feeds on seagrass for 60% of its food requirements. Bonnethead sharks eat seagrass along with snails, crabs, bony fish and shrimp.

As opposed to herbivores (plant eaters) and carnivores (meat eaters), omnivores are those animals which can eat both plant and animal matter. Seagrass is a marine, flowering plant and often create meadows on seabeds in some coastal waters. With this finding by the University of California researchers and those from the Florida International University in the US, we finally realize that the assumption of all sharks being carnivores is wrong!

The bonnethead shark is found commonly in the shallow waters of the Gulf of Mexico and the Western Atlantic ocean. These omnivorous sharks are not as large as per shark standards; but adult females which are larger than the males can grow to a length of five feet. Bonnethead sharks lack the kind of teeth best suited for chewing or mastication; so, to weaken plant cells, this omnivorous shark may rely on strong stomach acids so the enzymes can have their digestive effects.

Samantha Leigh, a study co-author and an expert in ecology and evolutionary biology at the University of California, Irvine, said, “Bonnetheads have a digestive system that is very similar to other closely-related species that are definitely strictly carnivorous, so the fact that they are acting like omnivores is truly remarkable.”

To determine if the grass is sustenance for the sharks, the scientist laced an aquatic laboratory with carbon-13, which is a traceable isotope that was taken in by the seagrass in the enclosure. The team then captured five wild bonnethead sharks near the Florida Keys and placed those sharks on a diet of 90% seagrass and 10% squid for three weeks. Finally, they found the isotope in the analyzed material along with plant-digesting enzymes in the guts of the sharks.

Study authors estimate that the seagrass compromises up to 60% of a bonnethead shark’s diet in the wild. Scientists plan to continue the study to determine if the bonnethead is specially adapted to eat seagrass or if other types of sharks are omnivorous as well. The real question is how this new discovery will impact the next Sharknado.